1. Field of the Invention
The present invention relates to a color selecting method, an image processing method, an image processing apparatus, and a recording medium for printing a color chart having a plurality of color patches with a printing machine, and selecting one of the color patches of the color chart which is closest to a designated color.
2. Description of the Related Art
With significant advances in inkjet technology in recent years, it has become possible for inkjet printers to produce large color prints of high quality at high speeds. Inkjet printers are not only popular for private or home use, but nowadays also are widely used in commercial applications. Inkjet printers make it possible to print on POP (Point Of Purchase) posters, wall posters, large-size mediums such as outdoor advertisements and billboards, roll mediums, and thick hard mediums.
There are a wide variety of print mediums (hereinafter also referred to as “mediums”) available for use in prints to meet various commercial demands. For example, such print mediums include paper mediums such as synthetic paper, thick paper, aluminum-evaporated paper, etc., resin mediums such as those made of vinyl chloride, PET, etc., and tarpaulin paper made of woven fiber cloth with synthetic resin films applied to both surfaces thereof.
Since prints for use as advertisements (print mediums which have been printed) are expected to be effective to arouse consumer's motivation to buy advertised products through visual sensations of the consumer, the color finish of such prints is of particular importance. Heretofore, there have been disclosed various color matching technologies such as a method of generating an ICC (International Color Consortium) profile, a method of adjusting a designated color, etc. as a print color managing means. Such color matching technologies are applicable not only to inkjet printers but also to all types of digital printers, including those based on electrophotographic and thermosensitive principles, together with their peripheral devices across the board.
The method of adjusting a designated color referred to above comprises a method of making fine color adjustments of an area of interest in an image in order to bring the color into substantial conformity with a given color (designated color) designated by a color sample of color chips, while maintaining the color balance of the image as a whole. There have been disclosed various methods of adjusting a designated color.
A method of selecting a plurality of candidate colors may be carried out by gradually changing the values of variables that can be controlled for print. Examples of such variables include device-depending data such as C, M, Y, K data, R, B, G data, etc.
For example, Japanese Laid-Open Patent Publication No. 200-217007 discloses a color selecting method of bringing the impression of a designated color displayed on a display device and the impression of a color printed by a printing machine into conformity with each other. Specifically, Japanese Laid-Open Patent Publication No. 2000-217007 discloses a display window displayed on the display device where the displayed color is changeable and a printed color chart of 27 colors, which are thought to be close to a designated color that is displayed (see FIGS. 4 and 5 of Japanese Laid-Open Patent Publication No. 2000-217007). The color chart is made of color patches printed in colors having different C, M, Y, K values.
In order to print a color closest to a designated color using a printing machine where the device-dependent data represent C, M, Y, K, it is necessary to determine optimum values for four variables of C, M, Y, K.
If a designated color falls outside the range of the gamut of a printing machine, it is physically impossible to reproduce the designated color. In such a case, the designated color is replaced with a certain color (i.e., a color closest to the designated color) within the range of the gamut, and a gamut mapping process is carried out taking into account the color balance of the overall image. To this end, it is necessary to select an optimum gamut mapping process (hereinafter also referred to as “mapping process”).
If an observational environment in which a print is formed and an observational environment in which the print is displayed are different from each other, then the difference between the observational environments have to be taken into consideration. Specifically, the types of observational light sources, the types of background colors, etc. have to be considered as variable factors, and the colors of color patches to be printed on a color chart need to be appropriately selected. In addition, selected colors may be different depending on color preference of each person.
Thus, the manner in which colors are presented varies depending on controllable variables (device-dependent data or mapping processes), and the manner in which colors are seen varies depending on the observational environment. For printing a color chart taking all the above items into account, the number of color patches to be printed needs to be increased because it is necessary to widen the color presentation range for increasing color choices and it is necessary to attain color resolution for more strict color selection.
For example, if the values on the axes of L*, a*, b* are to be independently selectable in 10 stages, then 103=1000 color patches are required. As the number of color patches increases, the burden on the operator for selecting colors also increases and the overall size of a color chart including those color patches becomes larger. Therefore, the efficiency with which the operator works is lowered, making it difficult for the operator to select desired colors.